Transparent optical switch

ABSTRACT

A transparent optical switch includes network management and performance monitoring using bit level information obtained by extracting selected information on a polling basis and analyzing the extracted information in the electrical domain. In one embodiment, a signal is injected into the switch fabric of the switch via a demultiplexing device. The injected signal is extracted at the output of the switching fabric via an N:1 switch and analyzed by a signal analyzer to verify input to output connections. In another embodiment, an optical switch includes first and second switch fabrics for 1:2 broadcast capability. In a further embodiment, an optical communication system includes a plurality of optical networks and a plurality of optical switches that cooperate to generate unequipped signals and to obtain autonomously switch-to-switch port connectivity information required for auto-topology discovery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/239,787 filed Sep. 29, 2005, which will issue as U.S. Pat. No.7,167,611 on Jan. 23, 2007, which is a continuation of U.S. patentapplication Ser. No. 11/058,519, now U.S. Pat. No. 7,158,696, which is acontinuation of co-pending U.S. patent application Ser. No. 09/775,429,now U.S. Pat. No. 6,862,380, which claims benefit of United Statesprovisional patent application Ser. No. 60/180,347, filed Feb. 4, 2000.The aforementioned related patent applications are herein incorporatedby reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

The present invention relates generally to communication systems, andmore particularly, to optical communication networks.

BACKGROUND OF THE INVENTION

Conventional optical networks generally include switch devices thatprovide a connection between an input port and an output port toestablish a channel between first and second optical links. Suchswitches typically convert the optical signals to electrical signals tomake the input/output connections. The switch examines the data streamat a bit level to perform network management and performance monitoringfunctions. For example, frame headers can contain source and destinationinformation used to route a constant bit-rate data stream in thenetwork. Performance monitoring can include examining selected overheaddata to detect and isolate errors within the network.

However, switches that convert data from the optical domain to theelectrical domain and back to the optical domain can create animpediment to achieving the bandwidths that developing opticalnetworking technologies potentially offer. For example, dense wavedivision multiplexing (DWDM) systems multiplex a series of opticalsignals having varying wavelengths into a single optical fiber. A fiberhas a plurality of parallel channels each associated with a particularwavelength. The channel wavelengths have a predetermined spacing tominimize certain effects, e.g., cross talk, and to maximize the numberof channels that a fiber can carry.

A switch interfaces with input ports and output ports to provide desiredsignal paths between selected input and output ports of two DWDMsystems. The switch typically provides network management, signalrestoration, provisioning, grooming and some level of signal monitoring.

Transparent optical switches refer to switches that do not convertoptical signals to electrical signals. An exemplary switch is shown anddescribed in U.S. Pat. No. 5,937,117, to Ishida et al., which isincorporated herein by reference. One disadvantage associated with knowntransparent optical switches is the limited ability to examine andextract necessary information carried within the optical signal. Thus,adequate network management, performance monitoring, and control withinthe optical network is relatively complex, costly, and unreliable.

It would, therefore, be desirable to provide a transparent opticalswitch having enhanced performance monitoring, network management andcontrol functionality.

SUMMARY OF THE INVENTION

The present invention provides a transparent optical switch for a wavedivision multiplexing (WDM) based network having optical pass throughpaths and optoelectronic signal conversion for client interfaces inaccordance with the present invention. This arrangement provides pathlevel signal control and performance monitoring. While the invention isprimarily shown and described in conjunction with a dense wave divisionmultiplexing (DWDM) system, it will be appreciated that the invention isapplicable to optical systems in general in which it is desirable toprovide optical signal pass through paths through a switch withefficient performance monitoring, network management, control and faultdetection. For example, the invention is applicable to WDM systemswithout optoelectronic conversion.

In one aspect of the invention, an optical network includes an opticalswitch that extracts predetermined optical data traffic on a pollingbasis. The extracted information is converted to the electrical domainand examined at the bit level. In one embodiment, the system can extractdata from input and/or output ports of the switch to verify connectionsthrough the switch. Selected data can be injected into the opticalswitch via input ports and extracted from output ports for analysis bysignal analyzers. This arrangement also enables performance monitoringof the optical data stream by tapping selected data.

In a further aspect of the invention, an optical switch includes firstand second switch fabrics for providing 1:2 broadcast capability. Eachswitch input port splits an input signal into a first signal received bythe first switch fabric and a second signal received by the secondswitch fabric. In normal operation, the same output port receives thefirst and second signals and selects only one so that if one of theswitch fabrics fails, the output port can select the signal from theoperational switch fabric. Thus, the first and second switch fabricsprovide redundancy.

The first and second switch fabrics can be used for bridging a signalfrom one input port to two output ports. The first switch fabricconnects an input signal to the first output port and the second switchfabric connects the same input signal to the second output port. In oneembodiment, the redundant switch fabrics are used for bridging bysacrificing the fabric redundancy.

In another aspect of the invention, an optical communication systemincludes first and second optical switches between which opticalnetworks, such as DWDM networks, are coupled. The switches and the DWDMnetworks combine to provide unequipped signal generation. In anexemplary embodiment, transponders are located at section terminationpoints in the DWDM networks. The transponders detect unequippedconnections and generate unequipped or so-called keep-alive signals tothe switch, which loops the signal back to an associated switch. Withthis arrangement, unequipped conditions are detected and so-called keepalive or unequipped signals are generated as needed without unequippedsignal generation within the transparent cross-connect system.

In a further aspect of the invention, an optical communication systemincludes transparent optical switches and a DWDM network. The DWDMnetwork inserts port ID information into signal overheads, for example,of data traveling to a first optical switch from a second switch.Similarly, the DWDM network inserts port ID information into signaloverhead of data traveling from the first switch to the second switch.In an exemplary embodiment, transponders associated with the DWDM portscan detect and insert port ID information. The first and second switchescan exchange port ID information to identify port connections betweenthe switches. This arrangement enables the optical communication systemto automatically determine the network topology, e.g., automatictopology discovery.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic depiction of a transparent optical switch inaccordance with the present invention;

FIG. 2 is a schematic depiction of a transparent optical switchproviding switch fabric connection verification in accordance with thepresent invention;

FIG. 3 is a schematic depiction of a transparent optical switchproviding output signal performance monitoring in accordance with thepresent invention;

FIG. 4 is a schematic depiction of a transparent optical switchproviding input and output signal performance monitoring in accordancewith the present invention;

FIG. 5 is a schematic depiction of a transparent optical switch havingfirst and second switch fabrics providing 1:2 broadcast capability forbi-directional connections in accordance with the present invention;

FIG. 6 is a schematic depiction of an optical communication systemhaving transparent optical switches and optical networks providingunequipped signal generation in accordance with the present invention;

FIG. 7 is a schematic depiction of an optical communication systemhaving optical switches and optical networks that combine to provideautomatic network topology discovery in accordance with the presentinvention;

FIG. 8 is a schematic depiction of an optical communication systemhaving an optical switch and optical networks providing fault detectionand isolation in accordance with the present invention; and

FIG. 9 is a schematic depiction of an optical communication systemhaving an optical switch and optical networks providing mulitplexing andswitching within the add/drop ports in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a portion of a dense wave division multiplexing (DWDM)communication system 100 having a transparent optical switch 102 inaccordance with the present invention. As used herein, transparent andnon-blocking optical switches refer to optical switches that do notconvert optical signals to electrical signals for signals that passthrough the switch, i.e., not add/drop signals. The switch 102 includesswitching fabric 104 that interfaces with a first set of output ports106 a-d and a first set of input ports 108 a-d coupled to a first DWDMnetwork 110. A second set of input ports 112 a-d and a second set ofoutput ports 114 a-d are coupled to a second DWDM network 116. The ports106,108,112,114, in combination with the switching fabric 104 providebidirectional communication between the first and second DWDM networks110,116.

The first set of input ports 108 receive respective channel data from afirst DWDM demultiplexer 118 and the first set of output ports providechannel data to a first DWDM multiplexer 120. The first multiplexer 120and the first demultiplexer 118 can form a part of the first DWDMnetwork 110. Similarly, the second set of input and output ports 112,114provide input and output channels to a second multiplexer 122 and asecond demultiplexer 124 associated with the second DWDM network 116.

The cross-connect 102 further includes add/drop ports 126 a-N thatconvert the optical signals from the switching fabric 104 to electricalsignals. In an exemplary embodiment, a SONET/SDH configuration is usedin combination with regenerator section and multiplex sectiontermination points RSTP, MSTP. As known to one of ordinary skill in theart, the Regenerator Section Overhead (RSOH) and Multiplex SectionOverhead (MSOH) are terminated and processed at the termination pointsRSTP, MSTP. Bytes at the termination points are used for network levelfunctions, such as performance monitoring, in-band data communication,and protection switching signaling.

With this arrangement, the DWDM networks are not integrated into theswitch 102 to provide multi-vendor compatibility. The transponderswithin the DWDM systems convert the closely spaced channels multiplexedwithin a single fiber to electrical signals and then converts theelectrical signals back to standardized optical signals. Due to theinnovative nature of wavelength multiplexing technology there is no onestandard for the closely spaced wavelength channels. Therefore, it isnot currently possible to use a WDM system from one vendor and pass asignal through a switch from another vendor and then pass it throughanother WDM system from yet another vendor. One way to enable equipmentfrom various vendors to interconnect the WDM systems is via standardsingle channel optical interfaces through an optical switch.

FIG. 2 shows further details of a transparent optical switch 102 havingconnection verification in accordance with the present invention. Theoptical switch can be substantially similar to that shown in FIG. 1, inwhich like reference numbers indicate like elements. The switch 102includes switch fabric 104 that interfaces with input and output portsIPa-N,OPa-N. A demultiplexing 1:N switch 128 is coupled to an opticalsignal generator 130, which can be provided, for example, as an OC-N(N=3, 12, 48, 192) generator. It is well known to one of ordinary skillin the art that OC-N refers to a standard SONET signal format and rate.The 1:N switch 128 provides a connection of respective signals to eachof the input ports IPa-N to the OC-N generator on a polling basis.

A multiplexing N:1 switch 132 is connected to each of the output portsOPa-N for providing signal information to a first signal analyzer 134,which can be an OC-N analyzer. A network management system 136 cancontrol the overall switch 102 functionality and connection verificationvia a switch control 138, which can be coupled to the switching fabric104, the switches 128,132 and the signal generators and analyzers130,134.

Input/output connections through the switch fabric 104 can be verifiedby selectively switching in, via the 1:N switch 128, a predeterminedsignal generated by the signal generator 130 on a polling basis, i.e.,one port at a time. In one embodiment, a relatively low speed, e.g.,OC-3 (155.52 Mb/s SONET signal), connection verification signal from thesignal generator 130 is provided to the input ports IP via the 1:Nswitch. This optical signal uses a frequency different from thefrequencies of the bearer signal at input port IP interfaces. Theinjected signal is extracted at the output ports OP after passingthrough the switch fabric 104 and is provided to the first signalanalyzer 134 on a polling basis via the N:1 switch 132. The signalanalyzer 134 can determine a bit error rate (BER) for the injectedsignal.

The switch control 138 coordinates the 1:N switch 128 and N:1 switch 132configurations. If the switch control 138 commands the 1:N switch 128 toconnect to input IPi and commands the switch fabric 102 to connect IPito OPj then it also commands the OC-3 generator to insert the expectedconnection information IPi-OPj within the OC-3 signal. Then the switchcontrol 138 also commands the N:1 switch 132 to select an output portOPj to the OC-3 analyzer 134. If the switch fabric 104 makes theconnection properly the OC-3 signal received at 134 will contain theIPi-OPj connectivity information. The proper connection is thenverified. If no signal is received or the received signal containsdifferent connection information misconnection is identified.

It is understood that one of ordinary skill in the art can readilyselect and multiplex/demultiplex a series of optical signal generatorsand analyzers to meet the bandwidth requirements of a particularapplication. It is further understood that the polling of inputs andoutputs can be varied to inject and extract selected signals and is notlimited to one input and/or one output at any one time. In addition, theterm switch, such as 1:N, and N:1 switch, is to be construed broadly toinclude devices that selectively provide at least one signal path forone or more input/output signals to facilitate polling of the inputand/or output ports.

FIG. 3 shows a switch architecture similar to that shown in FIG. 2 withthe addition of a signal splitter 140, which can form a part of the N:1switch 132, and a further signal analyzer 142. A multiplexer 144 can becoupled to the N:1 switch/splitter 132 to provide selected signals fromthe output ports OPa-N to the respective signal analyzers 134,142 on apolling basis.

A predetermined portion of channel data through the switching fabric 104can be tapped from the output ports OP to the N:1 switch 132. Bycontrolling the multiplexer 144, the tapped data can be analyzed by thefirst or second signal analyzer 134,142 depending upon the date rate ofthe channel under test, for example. It is understood that a variety ofsignal analyzers, e.g., OC-48, OC-192, may be needed based upon thetapped data bandwidth.

FIG. 4 shows a switch similar to that shown in FIG. 3 with the additionof an input side N:1 switch 146 and corresponding signal analyzer 148.With this arrangement, a desired portion, e.g., ten percent, of the dataincoming to the switch 102 can be tapped and analyzed. The input sidesignal analyzer 148, which receives the tapped data from via the inputside N:1 switch 146, can determine a BER for the tapped input data. Inthe illustrated embodiment, the input side N:1 switch 146 extractsincoming data from the input ports IPa-N on a polling basis, e.g., oneport at a time.

FIG. 5 shows a transparent optical switch 200 in accordance with thepresent invention having first and second switch fabrics 202 a,b forproviding 1:2 broadcast capability. The switch 200 is shown in a statein which a bidirectional port (IPi, OPi) is bridged to two ports (IPj,OPj) and (IPk, OPk). The output from the port IPi is connected to twoports OPj,OPk but in the receive direction of the I-th port (OPi) itreceives signals only from port IPj.

Input ports IPi, . . . IPj, IPk split input signals Ii, . . . Ij, Ikinto respective sets of first and second signals Iia,Iib, . . .Ija,Ijb,Ika,Ikb that are provided to the switch fabrics 202 a, 202 b. Inthe exemplary embodiment shown, the first signal Iia from the firstinput port IPi is handled by the first switch fabric 202 a and thesecond signal Iib is handled by the second switching fabric 202 b. Theremaining input signals are likewise split and sent to respective switchfabrics 202 a,b. The incoming signals are directed by the respectivefirst and second switching fabrics 202 a,b to particular output portsOPi-OPk. The output ports OP each include a switch for selecting aswitch fabric 202 a,b signal path.

The switching fabrics 202 a,b receive the input signals and route themto selected output ports via mirror manipulation. Controlling mirrors inan optical switch to route signals is well known to one of ordinaryskill in the art. In the exemplary embodiment shown, the first signalIia from the first input port IPi is connected by the first switchingfabric 202 a to the second output port OPj. The second signal Iib fromthe first input port IPi is connected by the second switch fabric 202 bto third output port OPk. Similarly, the first signal Ija from thesecond input port IPj is connected to the first output port OPi and thesecond signal Ijb is connected to first output port OPi. The third inputport IPk, is not connected to an output port.

In general, each output port OP receives the same signal that is splitby an input port IP from both switch fabrics and selects the operationalsignal. That way a failure of one of the switch fabrics does not affectthe signal at the receiving port. In this embodiment the redundantswitch fabrics are used to bridge a signal from one port to two outgoingports. Each output port OPi . . . ,OPj,OPk selects a signal from one ofthe switching fabrics 202 a,b for output by the switch. This arrangementprovides a one to two broadcast function by utilizing redundant switchfabrics 202 a,b.

Signal analyzers 134,142 can be coupled to the output ports OP, asdescribed above, to enable performance monitoring, for example, of thesignals from the switch fabrics. In one embodiment, switch informationcan be inserted into header information and verified by the signalanalyzers.

FIG. 6 shows a portion of an optical communication system 300, which canbe a DWDM system, detecting and generating so-called unequipped orkeep-alive signals in accordance with the present invention. In general,optical switches and DWDM networks work in concert to generate keepalive signals that can be looped back by the switches. When a switchport is connected to another switch port, but not currently carrying anybearer data traffic, an unequipped signal should be provided in theoutgoing direction so that the link is continuously monitored and madeready to be used instantaneously.

The system 300 includes a first optical switch 302 coupled to a firstDWDM system 304, which can be associated with a particular location suchas office A. The first DWDM system 304 is coupled to a second DWDMsystem 306, which is connected to a second optical switch 308 associatedwith office B. The first DWDM system 304 includes a DWDM multiplexer 309and a demultiplexer 311 along with first and second ports or sectiontermination points 310,312. The first DWDM system 304 further includes atransponder 314 that can detect unequipped conditions and generateunequipped signals.

The second DWDM network 306 similarly includes a DWDM multiplexer anddemultiplexer 316,318, transponder 320, and section termination points322,324. The second DWDM network 306 is connected to the second opticalswitch 308. Port-to-port connections between the first and secondswitches 302,308 enable bi-directional communication between Office Aand Office B.

In general, an unequipped signal is inserted into an output port of anoptical switch when the outport is not connected to another port withinthe same switch and carrying a live signal. For example, an unequippedsignal is inserted into a first output port OPi of the first switch 302when it is not connected to another port within the first switch.Similarly, an unequipped signal is inserted into a first output port OPjof the second switch 308 when this port is not connected to another portwithin the second switch 308.

In operation, the first DWDM port 310 inserts its port ID and unequippedstatus indication into a particular set of overhead bytes, for example,in the signal going towards the first switch 302. When the first switch302 output port OPi is not connected to another port within the switch,the corresponding input port IPi is connected, i.e. looped back, to theoutput port OPi. The inserted signal from the first port 310 in thefirst DWDM network 304 is thus received at the second port 312.

The signal overhead is examined to extract the port ID and if the firstDWDM network 304 finds the same ID at the second port 312 as the oneinserted at the first port 310 then the first DWDM network continues toinsert the unequipped signal status at the first port 310. If on theother hand, the same port ID is not received at the second or input port312, then the first DWDM network 304 determines that the output port OPiis no longer connected to the input port IPi at the first opticalswitch. The first DWDM network 304 then removes the unequipped statusindication at the first port 310 and allows the received signal from anoutput port 322 of the second DWDM network 306 to pass through the firstDWDM network input port 310 towards the input port IPi of the firstoptical switch.

The input port 312 passes through the signal received from the firstswitch output port OPi. However, the corresponding overhead informationis read at the second port 312 to check for a change in status.Similarly, the same action takes place at transponders at input andoutput ports 322,320 of the second DWDM network.

FIG. 7 shows a portion of a DWDM communication system 500 having firstand second optical switches 502,504 with automatic topology discovery inaccordance with the present invention. The first and second opticalswitches 502,504 are connected by a DWDM system 506. A signal path fromthe second switch 504 to the first switch 502 includes a series of portsincluding a switch output port D2, first and second DWDM ports C2, B1,and switch input port A1. Similarly, a path connecting the switches inthe opposite direction also includes a series of ports A2:B2:C1:D1, asshown.

In general, port ID information is inserted into the data signaloverhead packets, such as into J0 or another SOH, during travel to thedestination switch. As known to one of ordinary skill in the art, J0 andSOH are header formats specified in SONET and SDH standards. Theswitches 502,504 extract the port ID information, from which channelconnection information can be determined.

In an exemplary embodiment, each DWDM port includes an optoelectronictransponder that can convert optical signals to electrical signals andconvert electrical signals to optical signals. The transponders enablethe ports to insert port ID information within a particular set ofoverhead bytes in the electrical domain and to provide the signal inoptical format into the DWDM system. Thus, each port can insert IDinformation into the optical data stream and extract ID information fromthe data stream on a polling basis using signal generators and signalanalyzers as shown and described above.

In the illustrated embodiment, a first input port A1 of the first switch502 receives data from a near-end DWDM transmit port B1, which receivesdata from a far-end DWDM receive port C2. The first switch 502 transmitsdata to a near-end DWDM transmit port B2 via switch output port A2.

Similarly, a first input port D1 of the second switch 504 receives datafrom a DWDM port C1, which receives data from a further DWDM port B2.The second switch 504 transmits data from an output port D2 to a DWDMport C2. Each port, or one port having information on other ports, caninsert port ID information into the data stream. The optical switches502,504, via signal analyzers discussed in FIG. 3, can extract port IDinformation to obtain connection information on a polling basis. It isunderstood that receive/transmit ports, e.g., B1/B2 may have identicalIDs.

In this arrangement, the first switch 502 should determine that itsinput port A1 is connected to the output port D2 of the second switch504 without the second switch 504 having to generate any signal with theD2 port ID. The DWDM port C2 inserts its own ID in the particular set ofoverhead bytes allocated for this purpose. At the next DWDM port B1, theDWDM network then adds the first switch side port IDs B1,B2 in the sameset of overhead bytes. When the first switch 502 reads these overheadsbytes, it creates a 4-tuple ID A1:B1:B2:C2. The first switch 502 thensends this ID 4-tuple to the second switch 504 using an out of bandcommunication channel (not shown). Similarly, the second switch 504sends the D1:C1:C2:B2 ID 4-tuple to the first switch 502. When theswitches 502 and 504 send the messages they attach the switch IDs withthe port ID 4-tuples so that the receiving switch can identify theoriginator of the message.

The first and second switches 502,504 then broadcast this information toall other switches. Each switch with the received information from otherswitches and the ID information read from the incoming ports can thendetermine port connectivity. For example, the first switch 502 receivesthe concatenated ID information D1:C1:C2:B2 from the second switch 504and compares the last two entries in reverse order for a match. In thiscase, the first switch 502 finds that D1:C1:C2:B2 matches its ownconcatenated ID, i.e., A1:B1:B2:C2, from the input port A1. From thismatch, the first switch 502 determines the output port D2 of the secondswitch 504 is connected to a corresponding input port A1. A connectionbetween ports A2, D1 is similarly determined. Thus, this particularembodiment does not require the switches 502 and 504 to generate anysignals to determine connectivity. That is, this arrangement enablesswitches to exchange port connection information to determine thenetwork topology automatically.

FIG. 8 shows an optical communication system 600 including an opticalswitch 602 disposed between first and second DWDM networks 604,606 thatprovides enhanced fault detection and isolation in accordance with thepresent invention. The system should detect and isolate faults within areplaceable unit in the switch 602. Faults include both signal degradeand signal fail conditions. It is understood that the fault detectionand isolation does not need to be instantaneous.

Faults between the DWDM systems 604,606 are typically detected usingperformance monitoring at section termination points. It is thusnecessary to isolate faults to within a section A1-A2,A3-A4 between twoDWDM ports 604 and 606, for example. If performance monitoring isimplemented both at the input and the output ports A1,A2, then the faultis isolated within sections A1-A2, A2-A3 and A3-A4. If, however,performance monitoring is implemented only at the output port asdiscussed in FIG. 3, then the fault is isolated by correlation of theinternal signal (e.g. OC-3 in FIG. 3) performance and the bearer signal(e.g. OC-N in FIG. 3) performance at the output port. For example, ifthe OC-3 internal signal is good but the OC-N bearer signal is bad, thenthe fault is located in section A1-A2. If both the OC-3 and OC-N signalsare bad then the fault is in section A2-A3. If on the other hand bothsignals are good then the network management system, not shown, candetermine that the fault is in section A3-A4.

FIG. 9 shows an optical switch 700 having an add/drop port signalmultiplexer 702 in accordance with the present invention. The add/dropmultiplexer 700 may include an electronic switch to switch signalswithin the drop signals. The switch 700 includes pass through paths 704between first and second DWDM networks 706,708 and drop signal paths 710from the switch 700 to the add/drop multiplexer 702. The add/dropmultiplexer converts the optical signals from the switch to electricalsignals.

With this arrangement, a plurality of drop signals having a speed lowerthan the network transport speed can be multiplexed to achieve increasedefficiency and lowered costs. Increased efficiency and lower cost isachieved by using only one wavelength for the higher speed multiplexedsignal for the long distance WDM network. By having the ability toaccess the overhead bits within the signals dropped at the switch node,it is possible to detect fault on the connection of a signal thattraverses multiple optical switches on its path. Note that theintermediate nodes on the signal path do not have access to the overheadbits of the signal because it is passed through the switch withoutoptical to electrical conversion. With fast detection capability at theend switch of the signal path, the switch 700 can fast reroute thesignal through an alternative route when the original signal fails. Itis not necessary for the end switch to know where the fault occurred.

In another aspect of the invention, with automatic topology discoveryand bit level overhead access at drop ports, so-called fast provisioningcan be achieved on request by client routers, for example. In oneembodiment, an optical network can include control channels having atermination point in each optical network disposed between switches.These channels can provide a routing network for carrying fastprovisioning information, network management, restoration messages, andother control messages.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

1. An optical switch device, comprising: a switch fabric; a plurality ofinput ports through which incoming data contained in a bearer signalpasses to the switch fabric; a plurality of output ports through whichoutgoing data passes from the switch fabric; a demultiplexing devicecoupled to at least one of the plurality of input ports for injecting anoptical connection verification signal into the switch fabric; a signalgenerator coupled to the demultiplexing device for injecting theconnection verification signal into the switch fabric at a frequencythat is different from a frequency of the bearer signal; a multiplexingdevice coupled to at least one of the plurality of output ports; and afirst signal analyzer coupled to the multiplexing device for analyzingthe data injected by the signal generator.
 2. The device according toclaim 1, further including a second signal analyzer coupled to themultiplexing device and a multiplexer coupled between the first andsecond analyzers and the multiplexing device.
 3. The device according toclaim 1, wherein the switch fabric includes first and second switchfabrics.
 4. The device according to claim 3, wherein at least one of theplurality of output ports receives signals from each of the first andsecond switch fabrics.
 5. The device according to claim 4, furtherincluding at least one signal analyzer coupled to one or more of theplurality of output ports for analyzing data from the first and secondswitch fabrics.
 6. The device according to claim 1, further including anadd/drop multiplexer coupled to the switch fabric.
 7. The deviceaccording to claim 2, wherein switch information is inserted into headerinformation and verified by at least one of said first signal analyzerand said second signal analyzer.
 8. A method for achieving bit levelaccess to data in an optical switch, comprising: coupling a plurality ofinput ports through which incoming data contained in a bearer signalpasses to a switch fabric; coupling a plurality of output ports throughwhich outgoing data passes from the switch fabric; coupling ademultiplexing device to at least one of the plurality of input ports toinject an optical connection verification signal into the switch fabric;coupling a signal generator to the demultiplexing device for injectingthe connection verification signal into the switch fabric at a frequencythat is different from a frequency of the bearer signal; coupling amultiplexing device to at least one of the plurality of output ports andcoupling a first signal analyzer to the multiplexing device foranalyzing the data injected by the signal generator.
 9. The methodaccording to claim 8, further including verifying a connection betweenan input port of the optical switch and an output port of the opticalswitch.
 10. The method according to claim 8, further including couplinga second signal analyzer to the multiplexing device and a multiplexercoupled between the first and second analyzers and the multiplexingdevice.
 11. The method according to claim 8, wherein the switch fabricincludes first and second switch fabrics.
 12. The method according toclaim 11, wherein at least one of the plurality of output ports receivessignals from each of the first and second switch fabrics.
 13. The methodaccording to claim 12, further including coupling at least one signalanalyzer to one or more of the plurality of output ports for analyzingdata from the first and second switch fabrics.
 14. The method accordingto claim 9, wherein switch information is inserted into headerinformation and verified by at least one of said first signal analyzerand said second signal analyzer.
 15. A system for achieving bit levelaccess to data in an optical switch, comprising: means for coupling aplurality of input ports through which incoming data contained in abearer signal passes to a switch fabric; means for coupling a pluralityof output ports through which outgoing data passes from the switchfabric; means for coupling a demultiplexing device to at least one ofthe plurality of input ports to inject an optical connectionverification signal into the switch fabric; means for coupling a signalgenerator to the demultiplexing device for injecting the connectionverification signal into the switch fabric at a frequency that isdifferent from a frequency of the bearer signal; means for coupling amultiplexing device to at least one of the plurality of output ports;and means for coupling a first signal analyzer to the multiplexingdevice for analyzing the data injected by the signal generator.
 16. Thesystem according to claim 15, further including means for verifying aconnection between an input port of the optical switch and an outputport of the optical switch.
 17. The system according to claim 15,further including means for coupling a second signal analyzer to themultiplexing device and a multiplexer coupled between the first andsecond analyzers and the multiplexing device.
 18. The system accordingto claim 15, wherein the switch fabric includes first and second switchfabrics.
 19. The system according to claim 16, wherein at least one ofthe plurality of output ports receives signals from each of the firstand second switch fabrics.
 20. The system according to claim 19, furtherincluding means for coupling at least one signal analyzer to one or moreof the plurality of output ports for analyzing data from the first andsecond switch fabrics.